Electrospray ionization mass spectrometry (ESI-MS), especially at nanospray flow rates, has become very valuable for biological research because of its sensitivity and the ease with which it can be coupled with separation techniques such as liquid chromatography (LC). Typically, generating a stable electrospray at nanospray flow rates requires emitter tips with very small orifice diameters.
When fabricating the tips, both the inner and outer diameters can contribute significantly to the performance of the emitter tip at obtaining a stable nano-electrospray. Traditional methods for forming emitter tips can be associated with inner diameters that decrease along the length of the tip and/or with large outer diameters (i.e., blunt and/or thick walls) at the orifice. Thick walls at the orifice can adversely affect nanospray performance, and tapered inner diameters can contribute to clogging. Furthermore, many of the existing methods for forming emitter tips lack reproducibility and/or simplicity. Therefore, a need exists for a reproducible method of producing robust ESI emitter tips that are capable of nanospray and that resist clogging.